>>47861909She's prominent on a part of the game that's mostly story-driven and as such requires reading text to enjoy, which is a big no for a fanbase like pokemon. You can also see this in
>>47856498, Emma's sidequest, despite being better written than most things in the main series is largely ignored by the fanbase, but Zinnia's quest is kinda forced on you instead of being entirely optional like Emma's.
Not that Zinnia is great mind you but that's why she's hated, because she's too associated with a storyline.